Sealed tubular electrical resistance heater with ground connection

ABSTRACT

Tubular electrical resistance heater having a flexible heater element composed of a core with a resistance wire wound helically around the core and integral unheated terminal portions. The heater element is disposed in an open ended metallic tube with its unheated portions extending from within to without the tube where a lead wire is connected to the ends of the unheated terminal portions. A conductive ground wire is in electrical contact with the outer surface of said tube at a location corresponding to the unheated terminal portions of the heater element. A unitary moisture impervious sealing material encapsulates the end of the tube, the connection of the heater to the lead wire and the connection of the ground wire to the tube.

United States Patent [72] Inventor Rene D. Hebert Chlcopee Falls, Mass.

[21] Appl. No. 834,664

[22] Filed June 19, 1969 [4S] Patented July 13, 1971 [73] Assignee Springfield Wire, Inc.

Springfield, Mass.

[54] SEALED TUBULAR ELECTRICAL RESISTANCE HEATER WITH GROUND CONNECTION [561 Relerences Cited UNITED STATES PATENTS 2,193.017 3/1970 Bassett, Jr. 174/75C Primary Examiner- Volodymyr Y. Mayewsky Attorney Chapin, Neal and Dempsey ABSTRACT: Tubular electrical resistance heater having a flexible heater element composed of a core with a resistance wire wound helically around the core and integral unheated terminal portions. The heater element is disposed in an open ended metallic tube with its unheated portions extending from within to without the tube where a lead wire is connected to the ends of the unheated terminal portions. A conductive ground wire is in electrical contact with the outer surface of said tube at a location corresponding to the unheated terminal portions of the heater element. A unitary moisture impervious sealing material encapsulates the end of the tube, the connection of the heater to the lead wire and the connection of the ground wire to the tube.

PATENTED JUL 1 319w JIIIIJITI SEALED TUBULAR ELECTRICAL RESISTANCE HEATER WITH GROUND CONNECTION it is the principle object of this invention to provide an improved construction of electrical tubular heater with ground connection for use in wet locations whereby selection of materials for use in the various components of the heater is unhindered by concern for galvanic deterioration of dissimilar metals when used in the heater components.

It is another object of this invention to provide improved construction for grounded tubular electrical resistance heaters for use in moist locations using the most effective and economical means for overcoming galvanic deterioration of the contacting portions of the tubular sheath and ground connection.

Other objects and advantages of this invention will be more readily apparent from the following description and with reference to the accompanying drawings, in which FIG. 1 is a partial perspective view showing one end portion of a tubular heater, embodying this invention, before application ofa heater end seal;

FIG. 2 is a cross-sectional view of one end portion ofa tubular heater embodying this invention, and

FIG. 3 is a partial perspective view showing an end portion of a completed heater assembly embodying the invention.

In accordance with this invention a heater element which may be in the form of a wire or cable 4 is disposed in a metal sheath or tube 6. The heater cable 4 extends from within the tube OUlWfl-uly of its open end or ends, one of which is shown at 8 in FIG. I.

As will be appreciated by those skilled in the heater art, there are many types of tubular heaters, including among others, tubular defrost heaters. crankcase heaters, fiberglass insulated heaters, ceramic insulated heaters, cartridge heaters and the like. This invention may be applied to any type of tubular heater construction whether having one or two open ends, and from a reading of the disclosure, it will also be recognized that the ground connection described may be ap plied adjacent at least one of the open ends of any type of tubular heater.

in the embodiment shown the heater cable comprises a flexible core 10 which may be formed of any suitable heat resistant, thread, fibrous material or monofilament, such as asbestos, fiberglass or the like, A resistance wire 12 is wound helically around the core continuously over its entire length. At the terminal end portions of the core, bearing the resistance wire, there are provided cold terminal" sections indicated generally at 14 in FIG. 2.

In the illustrated embodiment, the cold terminal section 14 is formed by an electrically conductive ribbon, wire or strip 16 disposed longitudinally along the core and electrically interconnecting the overlying turns of the resistance wire 12 at the terminal end portion of the heating cable, whereby the terminal section of the heater is changed from a high-resistance, heat generating section, to a cold terminal" or nonheating section. Enclosing the core, the resistance wire and the conductive strip 16 is an overall insulatiompreferablyin the form of fiberglass braid. A heater of this type is disclosed in U.S. Pat. No. RE 26,522. Heater cable of this construction is of generally uniform diameter and flexibility and can readily be fitted into sheaths or tubes, such as shown at 6in FIGS. I and 2. Heaters of this type may be made in various lengths ranging from several inches to many feet in length and may be bent to any desired heater configuration.

Preferably the tubular element 6 is made of aluminum which possesses advantages of lightweight, high strength and low cost. The aluminum tubing when its open ends are sealed, as will hereafter be described, serves as a moistureproof housing for the fiberglass heater cable and also provides protection against abrasion and wear of the fiberglass insulation.

in the assembly of a heater, as shown in FIGS. l and 2, a short length of fiberglass insulation is removed for a short distance from the outer end portion of the cold terminal" section to expose a portion of the conductive strip 16, shorted turns of resistance wire 12 and their central supporting core 10. The length of insulation removed is usually on the order of a fraction of an inch to permit the application of a suitable mechanical connector 20 for connection of the heater wire to a lead wire 22.

As shown the connector has a first cylindrical, split-sleeve portion 21 clamped to the stranded conductor 24 of the lead wire 22 and a second such clamp portion 23 to fit around the end of the resistance wire. A third clamp portion 25 of larger diameter is fitted snugly around the outer surface of the end of the fiberglass insulation. The connector 20 may be tightly secured to these respective parts by the use of pliers or any other suitable tool. The purpose of the clamp portions 21 and 23 is to effect good mechanical and electrical connection of the lead wire and resistance wire and clamp portion 25 serves to increase the hold of the connector onto the heater cable 4. intermediate the portions 2i and 23 of the connector is a small web portion which separates these two portions of the connector. Moreover, it will be noted that the axes of sections 23 and 2i are on opposite sides of the web. The purpose of this arrangement is so that the conductor wire 24 will be spaced from the fibrous core element 10 of the heater cable 2, and with the application of a mold end seal these two components are hermetically sealed one from the other. In this way any moisture which might find its way along the conductor wire 24 tothe connector 20 will not be "wicked" into the heater by the fibrous core.

A ground connection is applied to the outer surface of the tube 6 adjacent an open end of the tube and comprises a suitablelead wire 26 which may be insulated with polyvinyl chloride, silicone, neoprene or the like, extruded over a stranded conductor element 27, preferably copper. The copper conductor 27 is held in intimate contact with the outer surface of the aluminum tube 6 by means of a suitable metal band'or clip 28 which is shown as a split cylindrical sleeve arrangement having a pair of circumferentially extending axially spaced slits 30 and 3!. The band 28 may be made of any suitable conductive material such as steel, copper, or a suitable copper alloy, such as /30 copper/brass, with copper or a copper alloy being preferable because of superior conductivityswhen the band is made of copper or an alloy thereof, it is also preferable that it be coated with corrosion resistant material, such as tin or nickel to prevent oxidation of the copper.

In the embodiment shown, the end of the conductor 27 is disposed under, over and then under the three spaced portions of the band 28 formed by the slots 30 and 31. In this way when the wire is in place and the band tightly clamped onto the tube, good electrical contact of the copper conductor wire 26 with theouter surface of the aluminum tube 6 is insured. in addition, this arrangement provides a mechanical connection to good tensile strength.

In accordance with this invention, the most effective and economical materials may be selected to form the tube 6, and ground conductor. in this connection aluminum is preferable for use in forming the tube 6 and copper wire is preferable as the best and most economical conductor for the grounding lead 26. Stranded wire is preferable where flexibility is desirable, as in the embodiment shown. Ordinarily in a moist condition: the use of dissimilar metals, such as these, are prescribed especially where, as in this case, electricity will be involved in the end use of the product. ln such cases any moisture acts as an electrolyte and the result is galvanic deterioration of the dissimilar metals. This problem is overcome in this case by moisture sealing or encapsulating with a unitary, homogeneous material the entire ground connection at the same time as the end seal is applied over the end of the tube and the splice between the lead wire 22 and the heater cable 4. in accordance with this invention, .the assembly shown in FIG. I is placed in a mold cavity of desired configuration and size and a suitable elastomer injected into the mold cavity and heated until cured and hardened. Suitable end seal materials include' natural rubber. neoprene. silicone rubber, suitable plastics including polyvinyl chloride and other similar materials. Prior to molding a suitable primer of bonding agent is applied to the assembly or the portion over which the sealing material is to be molded. This insures tight bonding to the primed surfaces, both metal and nonmetal.

As shown in FIG. 2, the unitary molded material encapsulates the open end of the tube from a point inwardly of the ground connection and band 28 to a point outwardly of the connector 20. Preferably the sealing material selected should be compatible with the insulation of the lead and ground wires. Neoprene has been found to give excellent results when used as the end seal with neoprene ground and lead wires.

Location of the connection of the grounding wire 26 to the outer surface ofthe tube 6 by means ofthe band 28 is adjacent the open end of the tube and in axial correspondence with the intermediate portion of the unheated the heater element 4 within the tube. asmuch as the end seal 34 constitutes a zone of low heat transfer as compared to the unencapsulated portion of the tube where the heat transfer of the tube is much greater. ln addition, end seal is not usually capable of withstanding protemperatures and may be melted, softened or otherwise damaged by excessive concentration of high temperatures within the end seal. Should this occur, the moisture impervious character of the heater would be destroyed, and such heaters would not therefore be acceptable for wet applications. The distance the cold terminal section [4 extends into the tube depends upon the watt density of wire, is that the cold terminal portion of the heater may be readily made of sufficient length so that the selected encapsucounter in the apparatus for which it is designed.

Having thus described the invention, what [claim is:

l. Tubular electrical resistance heater comprising a hollow aluminum tube, open at end, an insulated lead conductor wire connected to the unheated terminal section outwardly of the tube, an insulated ground wire having a copper conductor with a bare end portion, a conductive metal band clampingly retaining said bare tary, moisture impervious elastomeric material encapsulating the open end of said tube,

wardly beyond the inner end of the encapsulating material,

2. Tubular electrical reslstance heater as set forth in claim I generally parallel elastomeric material,

metallic, electrically conductive connector, said grounding band comprising a generally split sleeve band composed at said tube adjacent an open end thereof, said band having axially spaced circumferentially extending slots, said conductor of the ground wire threaded through said slots whereby the ground conductor is held in intimate electrical and firm mechanical engagement with said tube. 

1. Tubular electrical resistance heater comprising a hollow aluminum tube, open at at least one end, an insulated resistance heater disposed in said tube and having nonheating terminal sections extending from within to without said open end, an insulated lead conductor wire connected to the unheated terminal section outwardly of the tube, an insulated ground wire having a copper conductor with a bare end portion, a conductive metal band clampingly retaining said bare end portion in electrical contact with the surface of said metal tube adjacent said open end and at a location on said tube in axial correspondence with a nonheating terminal section, said ground conductor and tube being dissimilar metals, and a unitary, moisture impervious elastomeric material encapsulating the open end of said tube, the connection to said lead conductor wire and the portion of the ground conductor in contact with said tube, said nonheating terminal section extending inwardly beyond the inner end of the encapsulating material.
 2. Tubular electrical resistance heater as set forth in claim 1 in which said ground conductor and lead conductor extend in generally parallel relationship from the encapsulating elastomeric material, said lead wire being connected to the outer end of the nonheating terminal section by means of a metallic, electrically conductive connector, said grounding band comprising a generally split sleeve band composed at least in part of copper, fitted in clamping engagement about said tube adjacent an open end thereof, said band having axially spaced circumferentially extending slots, said conductor of the ground wire threaded through said slots whereby the ground conductor is held in intimate electrical and firm mechanical engagement with said tube. 